The present invention relates to a communication apparatus for sending and receiving speech by using a digital communication line as a communication channel, such as a portable telephone and a PHS.
While everyday conversation is performed by using a digital communication line such as a conventional portable telephone or PHS, only mutual conversation speech can be heard from the telephone. Conversation only by conversation speech is apt to become businesslike in any case. In order to implement conversation accompanied by an atmosphere, there have been several inventions so far, which intended to share background sound between talkers by sending conversation speech superposed on background sound by telephone.
For instance, JP-A-11-191796 specification shows a method of sending speech and background sound with their analog waveforms superposed.
However, the above conventional technique does not allow the receiving side to adjust or stop only background sound in the case where its volume level or the background sound itself is not desirable for a listener. Thus, there was a problem that the sending side was at a loss to determine what value volume of background sound should be set at. In addition, there was a problem that, as the sending side always had the right to decide whether or not to send background sound, the receiving side cannot reject receiving of the background sound from the beginning.
Moreover, it was also a problem that, as an ordinary telephone has band limitation on transmitted signals, background sound also had band limitation resulting in deteriorated tone quality.
Furthermore, in case of implementing the inventions so far by using a conventional portable telephone, the background sound sending side must speech-encode and send analog waveforms in which conversation speech and background sound are superposed, and the background sound receiving side must speech-decode and reproduce the above described encoded speech data. As the speech-encoding method adopted to a portable telephone enhances compression effect by utilizing properties unique to speech, it does not suit any encoding other than that of speech, such as background sound. Therefore, there was a problem that quality of background sound was lost in the case of implementing the conventional inventions for sharing background sound with a conventional portable telephone.